Full roast beef with trimmings dinner - what can I provide in lieu of the beef for a pescatarian?

It's a special occasion meal and I've been looking for a vegetarian substitute as I can't think of a fish that'd go well with Yorkshire puddings and the rest. But most seem to involve mushrooms and the person (that'd be my eldest) I'm trying to cater for doesn't like mushrooms!!

(Though I do know that is they aren't notable mushrooms them they have been eaten!!)

Cauliflower or broccoli cheese with a breadcrumb crust?Puff pastry wrapped leek & cheese?& apricot stuffing?Blue cheese and walnut tartlet?Might get away with Salmon as long as there is a parsley sauce or similar not gravy

Whenever I'm doing a big roast for guests that includes a vegetarian, I'm afraid I take the line of least resistance and buy a Higgedy Pie, which I serve with vegetarian gravy. All the accompaniments - cauliflower cheese, veg, roast potatoes, parsnips are veggie, so they don't go hungry.